The present invention relates to a charging device provided with a non-contact type discharge electrode that electrical charges a photoreceptor for electrophotographic image formation, and relates to an image forming apparatus including the charging device.
Conventionally in some electrophotographic image forming apparatuses, a charging device including a shield case with an opening and a non-contact type discharge electrode fastened therein electrically charges a photoreceptor for image formation. The charging device generates corona discharge (hereinafter this may be simply referred to as discharge) from the tip end of the discharge electrode with a high voltage applied thereto with respect to the photoreceptor, thus electrically charging the photoreceptor.
In the charging device, ionic wind generated during discharging lets air flow into the shield case through the opening, and lets the air circulate in the shield case. At this time, if dust flows into the shield case from the outside, the dust will adhere to the discharge electrode. Although dust adhering to a part other than the tip end of the discharge electrode does not pose a problem, dust adhering to the tip end of the discharge electrode will result in a failure in uniform discharge, i.e., nonuniform discharge, so that the surface of the photoreceptor will not be electrically charged uniformly.
To cape with this, as disclosed in JP09-230668A (Patent Document 1), some conventional charging devices including a discharge electrode let air flow into a shield case through a slit formed in a base thereof, thereby letting ionic wind flow toward an opening of the shield case to prevent dust from adhering to the discharge electrode.
In the discharge electrode described in Patent Document 1, however, slits provided in the entire bottom face of the case cause air to flow through the entire shield case, thus slowing down the air flow rate, and therefore ionic wind cannot be sufficiently exhausted to the outside of the shield case through the opening. As a result, air passing over the surface of the photoreceptor tends to flow into the shield case. Further, since air in the shield case is exhausted toward the photoreceptor through the opening, dust such as silica particles and toner particles floating around the photoreceptor will be sucked into the shield case through the slits. In this way, the conventional charging devices fail to prevent dust from adhering to the tip end of an electrode reliably, and therefore cannot resolve the deterioration of an image quality due to nonuniform discharge sufficiently.
It is an object of the present invention to provide a charging device capable of preventing dust from adhering to a tip end of a discharge electrode reliably and resolving the deterioration of an image quality due to nonuniform discharge sufficiently, and to provide an image forming apparatus including the charging device.